The disclosure relates generally to stationary blades, and more particularly, to a cooling structure for a stationary blade.
Stationary blades are used in turbine applications to direct hot gas flows to moving blades to generate power. In steam and gas turbine applications, the stationary blades are referred to as nozzles, and are mounted to an exterior structure such as a casing and/or an internal seal structure by endwalls. Each endwall couples to an end of the airfoil part of the stationary blade. Each endwall includes a core that extends outwardly from an end of the airfoil.
In order to operate in extreme temperature settings, the airfoil and endwalls need to be cooled. For example, in some settings, a cooling fluid is pulled from the wheel space and directed to internal end walls for cooling. In contrast, in many gas turbine applications, later stage nozzles may be fed cooling fluid, e.g., air, extracted from a compressor thereof. Outer diameter endwalls receive the cooling fluid directly, while inner diameter endwalls receive the cooling fluid after it is routed through the airfoil from the outer diameter. Conventionally, this routing is performed by passing the cooling fluid through an impingement insert (also known as a baffle) within a core opening of the airfoil and into a pressurized diaphragm that is separate from and positioned radially internal from the endwall. Once the cooling fluid is in the diaphragm, the cooling fluid is directed radially outward to a cooling circuit in the endwall. The endwall cooling circuit can take a variety of forms such as a pin-pedestal arrangement and/or a serpentine passage in the endwall that directs the cooling fluid to necessary portions of the cores thereof.
The diaphragm arrangement presents a number of challenges. One challenge is the physical space required for the parts that create the diaphragm require the turbine to be longer, or there may not be room for wheelspace sealing innovations such as near flow path seals. Creating the diaphragm is also a complex process in that it must fit in a very short/small space and requires complex machining (or other manufacturing steps) after the stationary blade is cast.